<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<script>
			var month = 30;
			if(month <1|| month>12 ){
				month = Number.NaN; 
//				如果符合条件,month = NaN

			var num = 3.15;
			}
			console.log(month);
			
//			保留一位
			console.log(num.toFixed(1));
		</script>
	</head>
	<body>
	</body>
</html>
